<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
   <style>
       div{
          width: 200px;
          height: 200px;
          border: 2px solid green;
          border-radius: 100px;
        }
   </style>
</head>
<body>
    <div></div>
</body>
</html>